It could be clogged milk ducts. It will go away soon. Just keep nursing and bare through it. I had this happen a few days ago and now I'm fine. I hate it when it happens! Sometimes your nipples just get sore.

You could try a nipple shield also

I would be sure her latch is correct. Breastfeeding shouldn't hurt. Maybe the first few seconds are painful sometimes but not the entire time. You can put coconut oil on your nipples on between feedings as well to help heal any damage. There are tons on videos online like YouTube to help you with latching.